Fibre optic cable, methods of manufacture and use thereof

Abstract

A fibre optic cable ( 500, 700 ) comprises retractable fibre units ( 502 ) extending in parallel with one another within an extruded polymer tube ( 504 ). The fibre units are free to slide in the tube such that a selected fibre unit ( 702 a ) can be accessed and re-directed by forming an opening in a wall of the tube ( 504 ) and withdrawing the selected fibre unit through the opening ( 710 ). Each fibre unit comprises two or more optical fibres ( 506 ) embedded in a solid resin material ( 520 ) to form a coated fibre bundle and an extruded polymer sheath ( 524 ). The fibre optic cable is manufactured by feeding the fibre units through an extrusion head ( 602 ) by which the extruded tube ( 504 ) is formed. The sheath ( 524 ) of each fibre unit is primarily polyethylene. A lining ( 510 ) of the extruded polymer tube is formed by polymer other than polyethylene, for example polypropylene.

The invention claimed is: 
     
       1. A fibre optic cable comprising a plurality of retractable fibre units extending in parallel with one another within a polymer tube, the fibre units being free to slide relative to one another and to the polymer tube such that a selected fibre unit can be accessed and re-directed by forming an opening in a wall of the polymer tube and withdrawing a length of the selected fibre unit through the opening, wherein each of said fibre units comprises two or more optical fibres embedded in a solid resin material to form a coated fibre bundle and a polymer sheath covering the coated fibre bundle, wherein the polymer sheath of each said fibre unit comprises primarily polyethylene (PE) polymer, wherein a lining of the polymer tube of the fibre optic cable is formed by polymer other than polyethylene, and wherein the polymer tube of the fibre optic cable comprises a co-extrusion of said lining within a main tubular body of a different polymer to the lining. 
     
     
       2. The fibre optic cable as claimed in  claim 1  wherein said lining of the polymer tube comprises primarily polypropylene (PP). 
     
     
       3. The fibre optic cable as claimed in  claim 1  wherein said lining of the polymer tube comprises primarily nylon. 
     
     
       4. The fibre optic cable as claimed in  claim 1 , wherein the polymer sheath of each said fibre unit comprises a mixture of PE polymer and one or more additives including a friction reducing material. 
     
     
       5. The fibre optic cable as claimed in  claim 1  wherein the material of said polymer sheath has a density of at least 935 kg/m 3 . 
     
     
       6. The fibre optic cable as claimed in  claim 1  wherein said PE polymer is at least partially cross-linked, a degree of cross-linking determined according to ISO 10147:2011 being in the range from 15% to 80%. 
     
     
       7. The fibre optic cable as claimed in  claim 1  wherein an inner surface of the polymer tube of the fibre optic cable has been formed with projections effective to reduce an area of contact between material of the tube and the fiber units. 
     
     
       8. The fibre optic cable as claimed in  claim 1  wherein said polymer tube is extruded with one or more strength members integrated in a main wall of the tube during extrusion. 
     
     
       9. The fibre optic cable as claimed in  claim 1  wherein, when said fibre optic cable is laid out in a generally straight route, a length of 100 m of a selected fibre unit can be withdrawn through an opening in the polymer tube at a speed greater than 1.4 m/s, without a pulling force exceeding the weight of a mass W, defined as the mass per kilometre length of the selected fibre unit. 
     
     
       10. The fibre optic cable as claimed in  claim 1  wherein, when said fibre optic cable is laid out in a generally straight route, a length of 100 m of a selected fibre unit can reliably be withdrawn through an opening in the polymer tube at a speed of 1.4 m/s, without a pulling force exceeding 5 N multiplied by the number of optical fibres in the selected fibre unit. 
     
     
       11. The fibre optic cable as claimed in  claim 1  wherein, when said fibre optic cable is laid out in a generally straight route, a length of 200 m of a selected fibre unit can be withdrawn through an opening in the polymer tube at a speed of 1.4 m/s, without a pulling force exceeding 5 N multiplied by the number of optical fibres in the selected fibre unit. 
     
     
       12. A method of manufacturing a fibre optic cable comprising a plurality of fibre units extending in parallel with one another within a polymer tube, the method comprising:
 (a) receiving said plurality of fibre units, each fibre unit having been manufactured previously and comprising two or more optical fibres embedded in a solid resin material to form a coated fibre bundle and a polymer sheath covering the coated fibre bundle, the polymer sheath comprising primarily polyethylene (PE) polymer; 
 (b) feeding said plurality of fibre units together as a bundle through a central opening in an extrusion die, while extruding said polymer tube through said die around the bundle, a lining of the polymer tube being formed by polymer other than polyethylene, the polymer tube of the fibre optic cable being formed by co-extrusion of said lining within a main tubular body of a different polymer to the lining; 
 (c) drawing said polymer tube and bundle through the extrusion die while controlling process parameters to draw and cool the polymer tube to have finished interior and exterior dimensions such that the fibre units remain loose within the polymer tube, 
 thereby producing said fibre optic cable such that a selected fibre unit can be accessed and re-directed by forming an opening in a wall of the polymer tube and withdrawing a length of the selected fibre unit through the opening. 
 
     
     
       13. The method as claimed in  claim 12  wherein said lining of the polymer tube comprises primarily polypropylene. 
     
     
       14. The method as claimed in  claim 12  wherein said lining of the polymer tube comprises primarily nylon. 
     
     
       15. The method as claimed in  claim 12  wherein the polymer sheath of each said fibre unit comprises a mixture of PE polymer and one or more additives including a friction reducing material. 
     
     
       16. The method as claimed in  claim 12  wherein the material of said polymer sheath has a density of at least 935 kg/m 3 . 
     
     
       17. The method as claimed in  claim 12  wherein said PE polymer is at least partially cross-linked, a degree of cross-linking determined according to ISO 10147:2011 prior to step (b) being in the range from 15% to 80%. 
     
     
       18. The method as claimed in  claim 12  wherein an inner surface of the polymer tube of the fibre optic cable is formed with projections effective to reduce an area of contact between material of the tube and the fiber units. 
     
     
       19. The method as claimed in  claim 12  wherein the solid resin material has a tensile modulus greater than 100 MPa. 
     
     
       20. The method as claimed in  claim 12  wherein said main tubular body is of polyethylene. 
     
     
       21. The method as claimed in  claim 12  wherein said main tubular body is extruded of medium density polyethylene (MDPE). 
     
     
       22. The method as claimed in  claim 12  wherein in step (b) said polymer tube is extruded with one or more strength members integrated in the main tubular body. 
     
     
       23. A method of providing fibre optic connections from a distribution point to a plurality of customer access points, the method comprising:
 (a) installing an optical fibre cable as claimed in  claim 1  extending from the distribution point and past the plurality of customer access points; 
 (b) for a customer access point, providing an opening in the tube wall of the fibre optic cable at a location convenient for the customer access point and withdrawing a length of a selected fibre unit through the opening; 
 (c) providing a branching duct from the vicinity of said opening to said customer access point; 
 (d) installing the withdrawn length of the selected fibre unit through the branching duct from the opening to the access point; and 
 (e) repeating steps (b) to (d) for successive customer access points, selecting a different fibre unit each time and forming a new opening or re-using an existing opening at a convenient location. 
 
     
     
       24. The method as claimed in  claim 23  wherein for at least one selected fibre unit the length of fibre unit withdrawn through the opening exceeds 100 m. 
     
     
       25. The method as claimed in  claim 23  wherein for at least one selected fibre unit the length of fibre unit installed through the branching duct exceeds 100 m. 
     
     
       26. The method as claimed in  claim 23  wherein for at least one customer access point in step (d) the selected fibre unit is installed through the branching duct by pushing. 
     
     
       27. The method as claimed in  claim 23  wherein for at least one customer access point in step (d) the selected fibre unit is installed through the branching duct by blowing.